Tracer diffusion in polyatomic liquids

Abstract

New tracer diffusion data are reported. These plus other recently published work provide a wide range of solute (monatomic and polyatomic species) size and solvent molecular type. A hard sphere model, making use of diffusion data from computer simulations on hard sphere fluid, predicts fairly well the diffusivities for the solutes in nonpolar solvents of compact molecules. The model fails for solvents of normal alcohols (except methanol) and of noncompact molecules. Stokes’ law is re-examined and found to be invalid except for solute molecules large compared to solvent molecules. The oft-quoted validity of Stokes’ law for self-diffusion is shown to be an accident of conditions under which the law is usually applied. Further verified is a recently published correlation formula relating tracer diffusivity, solvent viscosity, and particle size.